A diamond compact is a polycrystalline mass of diamond particles bonded together to form an integral, tough, coherent, high-strength mass having a diamond concentration of at least 70 volume percent. Representative U.S. patents on the subject of diamond compacts are: U.S. Pat. Nos. 3,136,615; 3,141,746; 3,239,321; 3,609,818; 3,744,982; 3,816,085; 3,913,280 and 3,944,398. A composite compact is a compact bonded to a substrate material, such as cemented tungsten carbide (see U.S. Pat. Nos. 3,745,623 and 4,063,909). Compacts may be used as blanks for cutting tools, dressing tools, and wear parts.
U.S. Pat. Nos. 3,831,428; 4,129,052 and 4,144,739 disclose wire drawing dies made with diamond compacts. A diamond wire die compact comprises an inner mass of polycrystalline diamond (as described above under the term compact) which inner mass is surrounded by and bonded to a mass of metal bonded carbide, such as cobalt cemented tungsten carbide.
The actual wire die is fabricated in a variety of ways and generally involves fitting or securing the wire die compact within a high strength metal ring and forming the wire drawing hole through the center of the polycrystalline diamond section using means well known in the art, such as a laser. The hole could then be finished by drawing a wire impregnated with diamond dust back and forth through the hole. The hole may be preformed during the high pressure-high temperature sintering process if the teaching of U.S. Pat. No. 3,831,428 at column 4 lines 54-60 and FIG. 4 is followed (predisposing a wire through the polycrystalline core which wire may be later removed by dissolving it in a suitable acid).
Dietrich South African Patent Application No. 77/5521 discloses a diamond wire die compact provided with a tantalum liner bonding the carbide annulus to the central polycrystalline diamond core. Dietrich claims that the tantalum layer effectively bonds the diamond core to the carbide surrounding it.
Both the Wentorf (U.S. Pat. No. 3,831,428) wire die compacts and those of Dietrich are made under high pressure-high tenmperature sintering processes in which a catalytic metal such as cobalt infiltrates radially from the surrounding metal carbide annulus or cylinder (so called sweep-through process). This catalyst accelerates the sintering process leading to extensive diamond-to-diamond bonding. The diamond compact quality is dependent upon the degree of diamond-to-diamond bonding in the microstructure. This bonding seems to be attainable when uniform and sufficient amount of cobalt is introduced into the grain boundaries during high pressure-high temperature (HP/HT) conditions with other factors being constant.
The major problem in making large size (e.g. 24 mm diameter) compact die blanks is the inefficiency of cobalt diffusion by a conventional radial sweep-through technique. Radial diffusion has been found to be inadequate to provide the desired cobalt concentration throughout the diamond core.
The research which led to the present invention was in an effort to improve the catalyst diffusion in the larger size die blanks and to decrease the percentage of defective blanks which result from the known processes. Defects occur mainly in the form of both poorly bonded areas in the diamond core and cracking in the diamond or in the metal carbide section. Cracking occurs erratically during various manufacturing operations, such as pressing, grinding of the outside diameter, surface grinding, lapping, and even under static conditions, making detection of the cause very difficult. Defects are also detected by x-radiographic examination. A secondary objective was to apply any successful technique to die blanks of smaller size.